1 /* SPDX-License-Identifier: GPL-2.0-only */
2 /*
3  * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
4  *
5  * Delay routines using pre computed loops_per_jiffy value.
6  *
7  * vineetg: Feb 2012
8  *  -Rewrote in "C" to avoid dealing with availability of H/w MPY
9  *  -Also reduced the num of MPY operations from 3 to 2
10  *
11  * Amit Bhor: Codito Technologies 2004
12  */
13 
14 #ifndef __ASM_ARC_UDELAY_H
15 #define __ASM_ARC_UDELAY_H
16 
17 #include <asm-generic/types.h>
18 #include <asm/param.h>		/* HZ */
19 
20 extern unsigned long loops_per_jiffy;
21 
__delay(unsigned long loops)22 static inline void __delay(unsigned long loops)
23 {
24 	__asm__ __volatile__(
25 	"	mov lp_count, %0	\n"
26 	"	lp  1f			\n"
27 	"	nop			\n"
28 	"1:				\n"
29 	:
30         : "r"(loops)
31         : "lp_count");
32 }
33 
34 extern void __bad_udelay(void);
35 
36 /*
37  * Normal Math for computing loops in "N" usecs
38  *  -we have precomputed @loops_per_jiffy
39  *  -1 sec has HZ jiffies
40  * loops per "N" usecs = ((loops_per_jiffy * HZ / 1000000) * N)
41  *
42  * Approximate Division by multiplication:
43  *  -Mathematically if we multiply and divide a number by same value the
44  *   result remains unchanged:  In this case, we use 2^32
45  *  -> (loops_per_N_usec * 2^32 ) / 2^32
46  *  -> (((loops_per_jiffy * HZ / 1000000) * N) * 2^32) / 2^32
47  *  -> (loops_per_jiffy * HZ * N * 4295) / 2^32
48  *
49  *  -Divide by 2^32 is very simply right shift by 32
50  *  -We simply need to ensure that the multiply per above eqn happens in
51  *   64-bit precision (if CPU doesn't support it - gcc can emaulate it)
52  */
53 
__udelay(unsigned long usecs)54 static inline void __udelay(unsigned long usecs)
55 {
56 	unsigned long loops;
57 
58 	/* (u64) cast ensures 64 bit MPY - real or emulated
59 	 * HZ * 4295 is pre-evaluated by gcc - hence only 2 mpy ops
60 	 */
61 	loops = ((u64) usecs * 4295 * HZ * loops_per_jiffy) >> 32;
62 
63 	__delay(loops);
64 }
65 
66 #define udelay(n) (__builtin_constant_p(n) ? ((n) > 20000 ? __bad_udelay() \
67 				: __udelay(n)) : __udelay(n))
68 
69 #endif /* __ASM_ARC_UDELAY_H */
70